Selective transfer of electrical oscillatory energy



Dec. 14, 1943. J. B. MlNTER, 2D

SELECTIVE TRANSFER OF ELECTRICAL OSCILLATORY ENERGY Fiied Aug. 50, 1940 2 Sheets-Sheet l INVENTOR ATTORNEY boo 0o Dec. 1.4, 1943.

J. B. MINTER, 2D

SELECTIVE TRANSFER OF ELECTRICAL OSCILLATORY ENERGY Filed 'Aug. 50, 1940 2 Sheets-Sheet 2 6 rule/vs 4 run/v.5 Eran/vs 0 v 450 KC I INVENTOR JrcyB. M 17/222273 2 ATTORNEY Patented Dec. 14,1943

SELECTIVE TRANSFER OF ELECTRICAL oscmAToar ENERGY Jerry B. Minter, 2nd, Mountain Lakes, N. J., as-

signor to Harry W. Houck, Livingston, N. J.

, Application August so, 1940, SerialNo. 354,782

' 2 Claims. (01. 178-44) This invention relates to .a. method and apparatusfor transferring energy in the form of electrical oscillations from one circuit or point to another. 7 More particularly it deals with the transfer of such energy which lies within a predetermined range or band of frequencies, to the more or less complete exclusion of energy lying without such band.

In the transmissionofelectrical oscillatoryenergy, it is frequentlyof great advantage to be able to provide means for the transfer of energy in a selective fashion, with respect to the frequency thereof. As an example of such, the

, transfer of energy between the anode circuit of one thermionic valve and the input circuit of one valve to the other,- or at least that the efliy ciency of transmission of the desired frequencies be many fold that of the undesired frequencies.

A transmission characteristic which is especially useful is one which will allow the transsired signals be delivered to the reproducing device of the system. I

Transmission circuits have been proposed for the foregoing purposes, but have suffered from various, defects and difllculties, such as varying efficiencies of transmission 'at different portions of the band of frequencies intended to be passed. thereby, inability to .vary the I width' of such passed-band over wide limits or to vary it to any mission of substantially zero energy at frequenquency, will then allow the transmission of substantially the entire amount of energy at any frequencies lying between this first and a second predetermined frequency, and then again will bar the passage of energy lying at frequencies higher than this second frequency. Additionally it is often desirable to be 'able toshift the transmission characteristics, so that the diiference between these two predeter'mined frequencies may be made to assume'varying values, by the shift of oneor both of the frequencies delimiting the region of effective transmission.

As one example of shift of transmission characteristics in the art of transmitting speech, music and other signals by means of electrical oscillations, it frequently is desired to provide circuits located either at the transmitter or at desired degree within such limits.,- Other difllculties have been the complexity of such transfer circuits and devices, entailing great precision and high cost of manufacture and rendering adjustment thereof very difficult, especially when such transfer circuits were incorporated into apparatus placed in the hands of the laity, such as in'the case of household radio receivers.

' One object of ,my invention is to provide a transmission device of the character described which shall be relatively simple and therefore easy and economical to manufacture in-quantities.

Another object is to provide such a device, wherein all oscillatory or tuned circuits shall have substantially the same natural resonant period and shall, be formed ofsubstantially identical components, whereby ease of production and simplicity of adjustment when once installed is promoted. Yet another object is to provide such a device wherein the width of the band of frequencies effectively transmitted therethrough may .easily be varied over wide limits, by a simple switching the receiver, or at both points, which circuits shall pass therethrough a band of frequencies varying in width from 1000 cycles to 20,000 cycles, and in-certain applications of the transmission of intelligence, such as in television, it

often is desired that. a much wider band of frequencies be transmitted. Of course in any case,

it is desired that frequencies lying outside the desired band be attenuated or suppressed to as action and without the need of altering theposition of various components with-respect to one another, such as is frequently done in systems of this type in order to vary the width of the frequency band passed thereby.

Another purpose of this invention is to provide 'a transmission device which shall have constant amplitude and linear phase shift over substantially the entire width of the band of transmitted frequencies.

Yet a further purpose is to provide such a deoccurs at predeterminedpoints, so that sharp and precise discrimination between frequencies lying adjacent such points maybemade, according to the direction'in which. they lie relative to these points.

Another object of my invention is to providev atransmission device having band pass. charac- :teristics which remain symmetrical, even through the width of the band be altered over wide limits.

An additional object is to obtain,' using only apparatus constructed of conventional components and therefore relatively inexpensive, sharp cut-off points and variable band pass effects,

which results hitherto have been obtained only.

with the use of elaborate, delicate and therefore relatively expensive means, such as circuits using piezo-electric crystals and, the like.

Yet another purpose of my invention is to provide a transfer circuit capable of passing a wide band of frequencies, which circuit shall be capable of quick and easy adjustment, so that all portions thereof will transmit a substantially identical band of frequencies. Furthermore, my invention allows such adjustment to, be readily made in such cases as household, radio and television receivers, without the need of elaborate and expensive equipment for this so-called peaking of the transmission circuits.

In order better to understand my invention,

reference is madeto the drawings hereunto a-ppended, wherein:

Figure 1 is a schematic illustration of a trans put circuit is confined to a single path.

Figure 3 shows schematically one form of my invention, allowing the band pass width to be varied.

Figure 4 is a circuit showing m invention as applied to the transmission of oscillatory energy from the output of one thermionic valve to the input of another valve, as for example in the beat frequency circuit of a radio receiver of the double detection or superheterodyne type, using a suitable intermediate frequency, such as for example, 450 kilocycles.

Figure 5 shows a family of transmission curves illustrating the variable band pass results obtained by the device shown in the circuit of Fig. 4. i

In Fig. 1 there are schematically shown two circuits, A and B. Energy is to be transferred frOm one of these circuits to the other. Both circuits are of the resonant type, circuit A including capacity [0 and inductance H while circuit B includes capacity l2 and inductance l3.

In each case the respective inductances and capacities are connected in parallel. Transfer circuit C is provided and comprises capacity l4 and inductance IS, in a serie connection. However,

besides the actual transfer of energy by means of the circuit C energy is also transferred between circuits A and B by means of the inductive or magnetic coupling shown by the dotted arrow 16. as well as by the capacitive or static coupling indicated by the dotted lines and capacity I1.

While circuits of the type shown in Figure 1' have been published, 'yet the art has been unable 1 successfully to employ such circuits in actual practice. Numerous attempts have been made to construct apparatus according to the diagram of Fig. 1, but invariably the transmission curves obtained by such apparatus have failed to corneglected, or else various methods havebeen eniployed to offset or neutralize these couplings, all of which methods have proven to be ineffective. I have found that it is impossible to obtain satisfactory results with the circuits of Fig. 1 even when couplings I6 and II are reduced substantially to zero values. Yet apparatus constructed with a transmission circuit basically according to this diagram,'when such spurious couplings are reduced to zero and when certain other changes hereinafter described are made,- yields results which are so markedly improved that a transmission device of this basic type, when constructed according to my invention becomes a very practical and efiicient device. The degree of improvement obtained by elimination of the spurious couplings and by further modifications hereinafter to be described is so very great as to be utterly unexpected. In the relatively long period of time which has elapsed since this basic transmission circuit, as shown in Fig. 1, was first published, the art has been completely unable to utilize in a practical fashion this transmission circuit, but by the employment of my invention,

I am enabled to construct transmission circuits of this basic type which will in use give actual results extremely close to those predicated by theory. The results which I have obtained have enabled me to construct practical apparatus, employing a modified form of thi relatively simple circuit and yet yielding results which hitherto have required extremely complex circuits such as those using a large number of individual frequency selective sections coupled to one another.

In Figure 2 I have indicated how circuits A, B and C can be completely shielded from one another, as by enclosing each circuit in an individual grounded shield or container shown in dotted lines. This container may be constructed so ascompletely to shield both the electrostatic and the electromagnetic lines of force proceeding from the components making up each one of the circuits. The construction of such shields is well known in the art, but for use with my invention, it is advisable that the degree of shielding be carried to the greatest possible degree that is practical. Apparatus has hitherto been constructed in which circuits A and B were each completely shielded per se. It was then assumed I that circuitC would act satisfactorily. However, I have found that further couplings will necessarily exist between the circuit C and other apparatus connected to circuits A and B, in such fashion that secondary couplings ultimately will exist between each of circuits A and B, and circuit 0. Even though such ultimate secondary couplings may be a very low value, yet they will be sufficient to render practical operation of thi transmission circuit a failure.

In Figure 3, circuit A is provided with a load resistance [8 and circuit B with a load resistance l9. These load resistances are preferably connected in parallel with each anti-resonant circuit, but it is possible to employ series connected resistances rather than shuntconnected resistances. Furthermore, it is possible so to construct inductan'ces II and l3'that each of these circuit: will have in itself sufficient resistance to act as a load. However, I have found that most satisfactory results will beobtained when the respective loads are lumped as much as possible and I are put in parallel with the tuned circuits, as illustrated in this figure. I have also here shown the input and output leads of circuit C as connectedto tops 20 and 2|, taken off upon induct-' ances H and I3 respectively. These taps-may be variable as indicated and by avariation thereof it is possible to vary the width of the band of frequencies passed between the circuits A and B.

In Figure 4, valve 22 and valve 23 are coupled by circuits according to my invention. Anode energy feed 24 and input circuit ground return 25 are as usual, and by-pass condenser 26 therebetween is to help reduce unwanted coupling.

Each inductance has 240 turns on a powdered iron core, so as to give a higher Q and better coupling when a lower tap is used for the connection thereto of the coupling circuit, and each has a value of about 0.7 millihenry. The number of turns in the various taps are schematically indicated upon the drawings by the numbers 2, 4, 5, and 8, and they are very small compared with the total turns in each inductance. The load resistances are of 100,000 ohms each, but the.exact values of these resistances as well as the values of the condensers, depend upon frequencies to be used, Q of the coils, and other factors hereinafter to be discussed. In general the capacities are chosen so that the tuned circuits will resonate at a single frequency such as at 450 kc.

In Figure I have shown the results actually obtained by measurement of a transmission device using a circuit according to the diagram of Figure 4 and it can be noted how the band pass width decreases as the turns are reduced in number, and how the respective tops of the graphs for the larger number of turns are nearly flat as shown at 21, so that equal transmission of various frequencies lying therein is obtained. When 2 turns are used, the various circuits may be readily tuned by the simplest means, even by ear in the case of a household radio receiver, since the pass action is now well peaked as shown at 28. Then when a greater number of turns are used, the circuits will continue to be correctly tuned. It is to be understood that the 'above values are merely illustrative of a certain embodiment of my invention and are not to be taken as in any way limiting the values of the various components to be used, which will vary according to principles well known in the art, and also according to special factors later herein discussed.

It would be possible to alter the position of the inductance taps so as to give a step-up action, in case that the circuits to be coupled are of very low impedance, such as valves of low output impedance. Connecting the plate and grid to lower respective taps upon the inductances also minimizes the efiect of detuning due to the variation in interelectrode capacity of the tubes under ure 5 more nearly square, i. e., tends to make the discriminatory action upon frequencies lying near the critical cut-oil points, more pronounced.

The use of iron core coils also permits so-called permeability tuning: adjustment of the inductance by moving the iron core in and out of the coil or by otherwise altering the effectiveness of the core. This method of tuning is especially practical for the circuits of Figures 3 and 4, since here there exist no mutual inductance values which would be altered by such changes in the inductance ofeach coil as would be the case for most circuits of the usual type, such as the circuit varying bias control, as in the case of automatic volume control receiver circuits and when replacing one tube by another one. The tube effective output and input capacities become relatively more important as the capacities l0 and i2 are made smaller, and the respective tube capacities become a larger percentage of the total capacity. These interelectrode capacities are also more troublesome variables in the case ofsome of the high transconductance pentode types of tubes, so that the use of lower taps may be desirable when such tubes are employed.

I have found it important to keep all the tuned circuits including the coupling circuit C of low resistance and to have the coupling between tap turns and the coils as near 100% as possible. The use of iron core inductances aids in obtaining this result, as well as giving a higher Q, which latter tends to make the corners of the curves of Figshown in Figure 1.

One element of my invention which is of very great importance is the use of the load resistances l8 and i9, connected respectively to the two circuits to be coupled to one another. Without the use of these loads, the transmission circuit fails to act properly, to such an extent that no practical results can in mostcases be obtained. Of course these resistances are not completely lumped, although so indicated for convenience in the drawings. As well known to those skilled in the art, the inductances and the valve circuits connected to the circuits, will in themselves possess l unavoidable resistances. The sli htresistance losses of the capacities may usually be neglected when modern low components are used. Whileit would be possible to select valves and coils which would together give the desired resistance effects, I prefer to make the efiect of these components so low that additional resistance must be used to raise the total resistance to the desired value, thus allowing adjustments of this total value to be made, since the precise value of resistance to be used for the optimum results cannot be exactly obtained by computation, although this latter will give a more or less close approximation thereto.

While as above explained, the optimum results may be obtained with my invention, when the elements are made adjustable over a slight range, yet it is possible to compute approximate values for these elements in designing a practical circuit, so that only slight adjustments will be needed when the transmission circuit has once been constructed in accordance therewith. A discussion of these methods of computation is here given.

In the following discussion-- a is the step-down ratio between the entire inductance coil and the portion thereof used to couple to circuit C.

:00 is twice times the frequency at the centre of the band to be passed, expressed in cycles.

w is twice times the width of the band in cycles.

0, L, R, and Q have their conventional meanings in the art.

For unity coupling inthe coil step-down action, we have but since the coupling can closely approach, but never reach unity, the actual tap for a desired bandwidth will difier slightly from that indicated by this formula, and may easily be'determined by one skilled in the art.

Since L, C, and R ar all variable, it may be necessary to assume values for certain elements and compute the other elements by the following formulae;

Since R represents the total or effective load resistor at each end of the transmission circuit, and since the factors and C are frequently the given ones, so that R is to be computed by means of formulae, it may be noted that R can be considered as composed of two portions, defined by the following equations, where Rb is the effective coupling circuit C. It is possible to minimize the shunt resistance effects of the valves themselves by making the anode and grid connections thereto from lower taps on the inductances, as previously explained.

While I have illustrated my invention by the description of certain examples thereof and certain applications, such illustrations are not exelusive, and the scope of my invention is only limited by the hereunto appended claims, since many modifications and adaptations will be apparent to those skilled in the art.

I claim: v

1. A device for selectively transferring oscillatory electrical energy, including a first input circuit wherein the energy is present, a second output circuit to which said energy is to be transferred and a coupling circuit connecting said first-mentioned circuits, said input and output circuits each comprising inductance, capacity and resistance in parallel and being anti-resonant to a predetermined frequency and said coupling circuit comprising inductance and capacity in series, being resonant to said predetermined frequency and being connected between points uponthe respective inductances of the input and the output circuits lying intermediate the ends thereof, the product of the respective inductances and capacities of said three resonant circuits being of the same electrica1 values, and a return path for said coupling circuit connected between one end of the input inductance and the-corresponding end of the output inductance, in which device the 'total effective resistance, R, in parallel with each of the input and output circuits, respectively, is determined according to the formula where L is the inductance of the respective circuit, w is twice 1r times the width of the band pass in cycles, and we is twice 1r times the frequency at the centre of the band pass, and in which device the actual resistance Rs, to be added externally to said input and said output circuits, respectively, is determined according to the formula RR; R" R where Rb is the effective equivalent shunt resistance of the respective input and output circuits before said external resistance has been added thereto.

2. A device for selectively transferring oscillatory electrical energy, including a first input circuit wherein the energy is present, a second output circuit to which said energy is to be transferred and a coupling circuit connecting said firstmentioned circuits, said inputand output circuits each comprising inductance, capacity and resistance in parallel and being anti-resonant to a pre-determined frequency and said coupling circuit comprising inductance and capacity in series, beingresonant to said predetermined frequency and being connected between points upon the respective inductances of the input and the output circuits lying intermediate the ends there-- of, the respective inductances and capacities of said three resonant circuit being of the same electrical values, and a return path for said coupling circuit connected between one end of the input inductance and the corresponding end of the output inductance, in which the step down ratio, a, between the entire inductance in the respective input and output circuits and the portion thereof used to effect coupling through said resonant coupling circuit is determined according to the formula in cycles, and in which device the capacity, C, is

determined according to the formula L Rw where R is the total effective shunt resistance of the respective resonant circuits, and inwhich' device the inductance L is determined according to the formula JERRY B. MINTER, 2ND, 

